PE15.1-4 | Fluids and Electrolytes — Glossary

The hourly equivalent of the Holliday-Segar maintenance formula: 4 mL/kg/hr for first 10 kg, 2 mL/kg/hr for next 10 kg, 1 mL/kg/hr for each kg beyond 20 kg.

A hypothalamic hormone released in response to increased plasma osmolality or hypovolaemia; acts on renal collecting ducts to increase water reabsorption, reducing urine volume during dehydration.

A calcium salt given IV to stabilise the cardiac membrane in hyperkalaemia with ECG changes; raises the threshold potential of myocytes, preventing arrhythmia without reducing serum potassium.

The external diameter of an IV cannula expressed in gauge (G) — higher gauge = smaller diameter. Age-appropriate sizes: neonates 24G, infants 22-24G, children 20-22G, adolescents 18-20G.

A surgical emergency caused by increased pressure within a closed fascial compartment; in IO access, may result from fluid leaking into the anterior tibial compartment; presents with swelling, tense calf, and pain on passive dorsiflexion.

Metabolic alkalosis from loss of Cl-rich, HCO₃-poor fluid (vomiting, loop diuretics), leaving relative bicarbonate excess; commonly co-exists with hypokalaemia and hyponatraemia from diuretic use.

A clinical state resulting from a deficit of total body water, typically due to excess losses (diarrhoea, vomiting, fever) exceeding intake; classified as no/some/severe by IMNCI.

Body fluid outside cells, comprising interstitial fluid (~15% body weight) and plasma (~5% body weight); constitutes ~40% body weight in neonates.

Leakage of IV fluid or medication out of the vein into the surrounding subcutaneous tissue; presents as local swelling, pain, and pallor during or after flushing; requires immediate cannula removal.

A battery-powered intraosseous drill device (Vidacare) used to insert IO needles with a rotary drilling motion; the standard IO device in most paediatric emergency departments; uses 15 mm or 25 mm needles depending on patient size.

The appearance of blood in the cannula chamber or hub when a vein is successfully punctured during IV cannulation; indicates the needle tip has entered the venous lumen.

The volume of water already lost before treatment begins, calculated as % dehydration × weight (kg) × 10 mL/kg; must be added to maintenance when writing fluid orders.

The cartilaginous zone of endochondral ossification at the epiphysis of long bones; located within 1 cm of the tibial tuberosity in children; IO needle must be inserted distal to this to avoid injury.

A formula for estimating daily maintenance fluid requirements in children: 100 mL/kg/day for first 10 kg + 50 mL/kg/day for next 10 kg + 20 mL/kg/day for each kg beyond 20 kg.

Serum potassium above 5.5 mmol/L; depolarises cell membranes, causing peaked T waves, widened QRS, and risk of fatal ventricular arrhythmia; requires immediate ECG assessment.

Serum sodium above 145 mmol/L, reflecting water deficit relative to sodium; causes cellular dehydration and is particularly dangerous in neonates and infants with poor free-water access.

A concentrated sodium chloride solution used in acute symptomatic hyponatraemia at 2-3 mL/kg IV over 15-20 minutes to rapidly raise serum sodium by 3-5 mmol/L and abort seizures.

Serum potassium below 3.5 mmol/L; hyperpolarises cell membranes, causing muscle weakness, ileus, and characteristic ECG changes (flattened T waves, U waves).

Serum magnesium below 0.7 mmol/L; impairs renal potassium conservation and causes refractory hypokalaemia; should be suspected and corrected whenever hypokalaemia fails to respond to replacement.

Serum sodium below 135 mmol/L, reflecting excess free water relative to sodium; classified by volume status (hypovolaemic, euvolaemic, hypervolaemic) to guide management.

Organic solutes generated by brain cells to maintain intracellular volume during chronic hypernatraemia; their persistence after rapid correction causes cerebral oedema when free water is restored too quickly.

International Liaison Committee on Resuscitation — the global body that synthesises resuscitation evidence and publishes consensus guidelines; ILCOR 2020 guidelines endorse IO as equivalent to IV for drug delivery in resuscitation.

Integrated Management of Neonatal and Childhood Illness — a WHO/UNICEF evidence-based protocol for assessing and managing common childhood illnesses including diarrhoea, pneumonia, and malnutrition at health-facility and community levels.

Fluid lost via skin evaporation and respiratory tract (not urine or stool); approximately 400-600 mL/m²/day in children; increased by fever, tachypnoea, and radiant warmers.

The extracellular fluid that surrounds tissue cells, constituting approximately 75% of the ECF; acts as a reservoir for fluid redistribution in dehydration.

Fluid contained within cells, accounting for approximately 40% of body weight in adults and 30-40% in neonates; the dominant reservoir of total body water.

A route of vascular access achieved by inserting a needle directly into the bone marrow cavity, which connects to the central venous circulation; indicated when IV access fails within 2 attempts or 90 seconds in a critically ill child.

A bolus of 5-10 mL normal saline injected after IO needle placement to confirm free flow and no extravasation, and after each drug delivered via IO to push the medication from the marrow cavity into the central circulation.

The volume of fluid required to replace normal ongoing losses (urine, stool, insensible losses via skin and respiration) in a healthy, euvolaemic child at rest.

Drawing back on the syringe after IO needle insertion to obtain bone marrow blood; confirms placement if positive, but absence does not exclude correct placement in a shocked child.

A catastrophic neurological complication of too-rapid correction of chronic hyponatraemia (> 10-12 mmol/L/day); causes demyelination of pontine and extrapontine neurons, presenting as locked-in syndrome or quadriplegia.

A standard peripheral IV device comprising a hollow plastic cannula mounted over a sharp metal introducer needle; once the vein is punctured, the plastic cannula is advanced into the vein and the needle withdrawn.

Tall, narrow, tented T waves on ECG; the earliest manifestation of hyperkalaemia, reflecting altered repolarisation from membrane depolarisation; progresses to wide QRS if uncorrected.

Inflammation of a vein wall, presenting as erythema, warmth, tenderness, and a palpable cord; caused by mechanical irritation, hypertonic fluids, or infection at an IV cannula site.

IMNCI fluid management for children with no dehydration: increased home fluid intake with ORS and continued feeding, with advice to return if signs worsen.

IMNCI fluid management for children with some dehydration: supervised oral rehydration at a health facility using reduced-osmolarity ORS 75 mL/kg over 4 hours, followed by reassessment.

IMNCI fluid management for severe dehydration: immediate IV Ringer's lactate 100 mL/kg over 3 hours (> 12 months) or 6 hours (< 12 months), with hospitalisation and monitoring.

A falsely elevated serum potassium from in-vitro haemolysis of blood sample or delayed analysis; should be suspected when hyperkalaemia is unexpected and the clinical picture does not match.

A WHO-standard oral rehydration solution with osmolarity 245 mOsm/L (Na⁺ 75, Cl⁻ 65, glucose 75, K⁺ 20, citrate 10 mmol/L); reduces stool output and vomiting compared with the older standard ORS (311 mOsm/L).

The electrical potential difference across a cell membrane at rest (~−90 mV in myocytes), determined largely by the intracellular to extracellular potassium ratio; altered by potassium disorders to produce electrophysiological dysfunction.

A balanced crystalloid IV solution containing Na⁺ 130, K⁺ 4, Ca²⁺ 3, Cl⁻ 109, lactate 28 mmol/L; preferred over normal saline for paediatric IV rehydration as it is more physiological and avoids hyperchloraemic acidosis.

The great saphenous vein runs just anterior to the medial malleolus at the ankle — a reliably located peripheral vein accessible for cannulation when upper limb veins are inaccessible.

Syndrome of inappropriate antidiuretic hormone secretion — euvolaemic hyponatraemia with inappropriately concentrated urine (urine Na > 20 mmol/L, urine osmolality > plasma); treated with fluid restriction.

A bedside sign of dehydration assessed by gently pinching abdominal skin; returns in < 1 second normally, 1-2 seconds (slowly) in some dehydration, > 2 seconds (very slowly) in severe dehydration.

A cation-exchange resin given orally or rectally to increase faecal potassium excretion; used in mild-moderate hyperkalaemia without ECG changes; onset over hours, not suitable for emergencies.

The bony prominence on the anterior surface of the proximal tibia where the patellar tendon inserts; used as the anatomical landmark for proximal tibia IO insertion — the IO needle is inserted 2-3 cm below this point on the anteromedial surface.

The total water content of the body, expressed as a percentage of body weight; ranges from ~85% in premature neonates to ~60% in adult males, decreasing with age as fat mass increases.

Movement of potassium between the intracellular and extracellular compartments without change in total body potassium; driven by pH changes (acidosis shifts K out; alkalosis shifts K in), insulin, and beta-agonists.

A positive ECG deflection following the T wave; pathologically prominent in hypokalaemia, caused by delayed ventricular repolarisation; a marker of significant potassium depletion.

A constricting band applied proximal to the cannulation site to obstruct venous return, engorging the vein and making it more visible and palpable; should occlude venous flow but not arterial flow.